Motor-driven tuning control for radio receivers



FfHlMMER Dec. 6, 1949 MOTOR-DRIVEN TUNING CONTROL FOR RADIO RECEIVERS Filed June 20, 1947 WiL/4MM Patented Dec. 6, 1949 MOTOR-DRIVEN TUNING CONTROL FOR RADIO RECEIVERS Frank Himmer, Philadelphia, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application June 20, 1947, Serial No. '755,881

(Cl. Z50-36) 2 Claims. l

The invention herein described and claimed relates of a tuning system for radio communication apparatus, and in particular to an improved tuning system for superheterodyne radio receivers.

While the components comprising the new tuning system may all be placed at the same location, and, if desired, may all be contained in a single housing, the improved system may be most advantageously employed for controlling the tuning of a superheterodyne radio receiver from a remote location. Wire or cable connections are employed between the receiver and the remote control point, but no mechanical connection is required. The invention may consequently be employed, to considerable advantage, in radio receiving apparatus intended for installation in automobiles, airplanes, motorboats, and other form of mobile craft since, in mobile installations, it is frequently desirable to mount tuningcontrol means for the radio receiver on or near the instrument or driving-control panel while the radio receiver is desirably placed elsewhere in the vehicle or craft.

In accordance with a preferred embodiment of the invention, improved means are provided for automatically tuning the local oscillator of the receiver to the resonant frequency of a tuned or frequency-selection circuit located at a remote control position and their selected by the operator. The operator may make the selection automatically by depressing a station-selector pushbutton; or the selection may be made manually at the remote location by depressing a Manual pushbutton and adjusting a manualtuning control knob to the desired position, as shown by a manual-tuning indicator dial. The tuner of the receiver is motor driven by a suitable electric motor, located, if desired, within the housing of the radio receiver. In the receiver illustrated in the drawing, the tuner is comprised conventionally of theI variable inductances of the tunable circuits of the R.F. amplifier, mixer, and local oscillator stages of the receiver. A portion of the output of the local oscillator is applied, by way of a shielded or other suitable conductor, to the remotely-located tuned circuit selected by the operator; and the voltage developed across a portion of the selected remote tuned circuit is detected, fed back to the receiver as a control signal, and utilized to control the operation of the tuner motordrive.

It is an object of this invention to provide, for a superheterodyne radio receiver, an improved tuning system which includes tuning-control means adapted to be coupled to the receiver by electrical connections, without necessity of me chanical linkage.

It is another object of this invention to provide a superheterodyne radio receiver, capable of being controlled from a remote location, by station-selector pushbutton, and/or manual, tuning means, without employment of mechanical coupling between the remote tuning-control means and the radio receiver.

It is a further object of this invention to provide, for a superheterodyne radio receiver, improved means for automatically tuning the frequency of the local oscillator of the receiver to substantially the resonant frequency of a tuned circuit located in a remote tuning-control position and there selected by the operator by either pushbutton, or manual, tuning means.

These and other objects, features and advantages of the present invention will become clear from a consideration of the following detailed description of a preferred embodiment illustrated in the single figure of drawing.

Referring now to the drawing, there is schematically represented a superheterodyne radio receiver I0 including an R.F'. amplier I I, a frequency converter I2 comprised of a mixer section I3 and a local-oscillator section I4, an I.F. ampliiier I5, a second detector, AFC circuit, and first audio amplifier I6, a push-pull audio-frequency power amplier I'I, and a loudspeaker I8. The local oscillator I4 is represented schematically as being comprised, conventionally, of a section of a pentagrid-converter tube, an oscillator-plate voltage dropping resistor 2l, a bypass capacitor 22, a grid leak 23, a grid capacitor 24, and a tunable network 25 consisting of variable inductance 26 and capacitor 21. All of the components mentioned thus far are conventional and require no further description, either with respect to structure or manner of operation.

In accordance with the present invention, for purposes that will become clear, means are provided for deriving, from local oscillator I4, a portion of the R.F. oscillator voltage appearing across tuned circuit 25. Means are also provided for deriving, from the said oscillator, the unidirectional voltage developed across grid leak 23. Various means may lbe employed for these purposes; the means shown in the drawing, and about to be described, merely constitute the preferred manner of accomplishing the derivations. In the illustration, a portion of the R.F. oscillator voltage is derived by means of pickup coil 28 mutually coupled to oscillator coil 26; capacitor I9 provides an A.C. ground connection for the low-potential end of the pickup coil. In the illustration, the unidirectional voltage is derived by way of an isolation or lter circuit 29, comprising series resistors 3G, 3l andshunt capacitor 32. Resistor 3o isolates capacitor 32 from the oscillator; and resistor 3| isolates capacitor 32 from pickup coil 28.

In accordance with the presentV invention, receiver IS also includes a tuner motor 33, a tunermotor control tube 34, a tuner-motor control relay 35, a reversing-switch selector relay 36, a

tuner-actuated motor-reversing switch 37, and aY tuner-actuated manuel-tuning correcting switch 38. The functions of these components willi become clear as the description proceeds,

The plate of tuner-motor control tube 3d is shown to :be connected to a source of positive potential, B+, through coil 39 of tuner-motor control relay 35. The cathode of control tube 34 is connected to ground through resistor I8, and is also connected to the cathode-biasing network 40 of push-pull amplifier il. The grid of tube 34 isalso connected tothe push-pull amplifier biasing' network 4S, but is connected by way of resistor 'l5 of thev remote'tuning-control unit te. The remote tuning-control unit will be described hereinafter.

Tuner-motor control relay 35 is a double-pole double-throw relayI comprising a coil 39 and two double-throw switches 4l and 42.

Tuner motor 33 isA a reversible, shunt wound, D.-C. motor comprising an armature 46 and a center-tapped shunteeld winding 4l. The motor is' mechanically coupled, through a magnetic clutch #it and through suitable reduction gearing (not shown), to thereceiver tuner comprised, conventionally, of the.` variable inductances i9, 20 and 26 of the tunable circuits of R.-F. ampli- :der ll, mixer section1l3 and localr oscillator section i4,- respectively, In the drawing, the mechanical coupling between the three-unit tuner and motor 33 is indicated by the dotted-line representation 45.

. The reversing-switch selector relay 35 is a three-pole double-throw relay comprising a coil 48 and three double-throw switches 49, 5U and 5i.

Variable inductances i9, 2Q and 2B are ganged 1 and may comprise an integral multi-unit tuner structure having three coils. mounted, conventionally, in parallel axial relation to each other. Each coil has a core of iron or other suitable material, usually a powdered core ofY high mag- 1 and inasmuch as the structural arrangement does not constitute, perse, the present invention, it is deemed suiiicient to illustrate schematically the manner in which switches 31 and' 38 operate.

It will be assumed that actuating-arms 52, 5S, 54 and 55 are moved to the right, in the drawing, when the tuner cores are moved in a frequency-increasing direction, and that the actuating-arms are moved to the left when the tuner cores are moved in a frequency-decreasing direction. The actuating-arms may conveniently be so positioned that as the tuner cores reach the high-frequency limit of the core stroke, actuating-arms 52 and 5t come into engagement with the movable contact-arms of switches 3l' and 33, respectively, to move the switch arms to their right-hand positions; and as the tuner cores reach the low-frequency limit of the core stroke, the movable contact-arms of switches 3i and 38 are engaged by actuating-arms 53 and 5t, respectively, and the switch arms are moved to their left-hand positions.

After the contact-arm of switch 3l has been moved to the right-hand position, at the Ihighirequency limit of the core stroke, the remains in the right-hand position until engaged by actuating-arm 53 and moved to the 1cit-hand position at the low-frequency limit of the stroke; it then remains in the left-hand .position until moved. But the movable contact-arm of switch 3,8 makes Vbut momentary closed contact at both the high-frequency and low-frequency limits of the stroke, being returned to a normally open position by spring S.

The means by which the timing of receiver it may be controlled from a remote location without employment of mechanical linkage between the receiver and the remote control point will now be described.

In the drawing, there is shown a tuning-control unit 5S comprising seven mechanically interlocking pushbuttons, l-T. Pushbuttons |-5 are used to select automatically preselected stations. Pushbutton 5 is the Manual button and is depressed when manual tuning is to be employed'. Pushbutton 'i is the Off button and is depressed when it is desired to turn 01T the receiver. In the illustrated tuning-control unit, there is no On lpushbutton, and depressing any one of pushbuttons i-'turns on the receiver. The tuning-control unit 65 is shown to be connected to receiver It by means of a shielded conductor il and a six-conductor -cable l5; all seven conductors may be under a common sheath, if desired.

Associated with station-selector pushbuttons lare adjustable inductance elements, 6|-65; and associated with Manual pushbutton 6 is a manually variable inductance element 66 operatively connected to a manual-tuning control knob (not shown) and to a manual-tuning indicator or dial 58. The manual-tuning control knob is mechanically coupled to a manually-operated reversing switch 69 through a frictional clutch (not shown) so that when the control knob is initially moved in a given direction, the movable contactarm of reversing switch 69 moves in the same direction. For example, when the manual-tuning control knob is first turned in a clockwise direction, the arm of reversing switch 59 is moved to the right-hand position. Further clockwise rotation of the control knob does not affect the position of the switch arm, but when the control knob is turned in the reverse direction, i. e., counterclockwise, the contact-arm of switch 69 immediately moves to the left-hand position.

The Ofi pushbutton 'l is connected in conventional manner between the iilament and power supply circuits of the radio receiver it and a source of external A.-C. or D.C. voltage 1i). In the case of an automobile radio, voltage source may conveniently be a six-volt storage battery, as illustrated in the drawing.

In the drawing, pushbuttons I-5 are double make-contact switches; pushbutton 5 is a double make-and-break contact switch; and pushbutton 1 is a double break-contact switch. One makecontact of each of pushbuttons I-E is connected, by way of shielded conductor 1I, to pickup coil 28 of local oscillator I4. The other make-contact of each of pushbuttons I--6 is connected, by way of one of the adjustable inductances EI-SB, associated with the particular pushbutton, to the grid of a plate-detector triode 12 which, together with grid capacitor 13, lter capacitor 14 and plate resistor 15, connected as shown, is included within the housing of tuning-control unit 60. The plate-circuit leads of tube 12, the leads from the xed contacts of reversing switch 59, a lead from one of the break-contacts of pushbutton 6, and a lead from Off pushbutton 1, go to the radio receiver I0 and are shown to be placed in a common cable 16.

The operation of the improved tuning-control means of the present invention will now be described.

To make the operation of the improved tuning system more readily understood, various operating conditions will be assumed in sequence. It will be assumed rst that, as the description starts, the receiver shown in the drawing is not operating, having been turned oil in the manner provided, namely, by depressing the Oi pushbutton 1. Control relays 35 and 36 are therefore shown in de-energized positions.

Assume now that station-selector pushbutton 2 is pressed to tune in automatically a, station having a carrier frequency oi say 650 kc. When pushbutton 2 is pressed, the Off pushbutton 1 is released since, in the receiver illustrated, all seven pushbuttons are mechanically interlocking (not shown) and only one of the pushbuttons is maintained in depressed position at a time. Assume that before pushbutton 2 is pressed, the receiver, altho not turned on, is tuned to say 550 kc., which is lower than the frequency of the station associated with station-selector pushbutton 2.

In the situation described above, when the receiver is turned on by depressing pushbutton 2, plate-detector tube 12, in the remote tuningcontrol unit 6B, remains non-conductive, being biased beyond cut-oi by the application to its grid of the negative D.C. voltage developed across grid leak 23 oi the receivers local oscillator I4. The voltage developed across grid leak 23 at receiver` I8 is applied to the grid of detector tube 12 at control unit B, by way of isolating or lter circuit 29 located at the receiver lil, shielded conductor 1I connecting receiver I0 to control unit 60, the cle-sed contacts of pushbutton 2, and inductance 62 associated therewith.

When, as has just been described, detector tube 12 is biased beyond cut-oil and is non-conducting, control tube 34 at receiver I0 conducts by reason of having a Zero bias applied thereto. The bias voltage on control tube 34 is zero due to the fact that the unidirectional voltage appearing across biasing network 4I) of the push-pull amplifier Il is applied both to the grid and to the cathode of tube 34. Plate current of control tube 34 flows through coil 39 of control relay 35, causing the movable contact-arms of switches 4I and 42 of relay 35 to move to the upper-contact positions. When this occurs, current from voltage-source 1G flows through coil 48 of relay 36 by way of the :closed contacts of "OT pushbutton 1, the upper contact of switch 42 oi relay 35, and the lower contacts of Manual pushbutton 6. The movable contact-arms of switches 49, 50 and 5l of relay 36 then move to the upper-contact positions. With the contact arms of switches 49 and 50 in the upper positions, a circuit is completed, either through the upper or lower portion of the centertapped iield winding 41, depending upon whether the movable contact-arm of switch 31 is in the left-hand or right-hand position. Assume, for the purpose of the example now being described, that the arm of switch 3l is in the left-hand position; current then iiows through the upper portion of eld winding 41. Assume further that, when current flows through the upper portion of field winding 41, motor 33 rotates in a direction to move the three cores of the multi-unit tuner in a frequency-increasing direction, it being understood that the direction of rotation of reversible motor 33 is determined by whether the current flows through the upper or lower section of field winding. Then, in the example now being described, it will be seen that, when pushbutton 2 is pressed, the motor-driven tuner moves in a direction to increase the frequency oi the R.F. mixer and local oscillator stages. A portion of the oscillator R.F. voltage is picked up by pick-up coil 28 and applied, by way of shielded conductor 1I, across the series-tuned circuit 62, 13 associated with the depressed station-selector pushbutton; and the R.F. voltage thus appearing across capacitor 13 is applied to the grid of platedetector tube 12. In the present example, motor 33 continues to rotate in the frequency-increasing direction until the frequency of local oscillator I4 coincides substantially with the frequency of the series-tuned circuit 62, 13 associated with depressed pushbutton 2. The circuit constants are so chosen that when the frequency of local oscillator I4 reaches substantially the resonant frequency of the selected series-tuned circuit, in the present example, the tuned circuit associated with depressed pushbutton 2, the peaks of the R.-F. voltage on the grid of tube l2 rise above cut-off and tube 12 conducts. When tube 12 conducts, the voltage developed across resistor 15 in the plate circuit of tube 12 is suiiicient to bias control tube 34 below cut-ofi and tube 34 ceases to conduct. Control relay 35 thereupon becomes de-energized and the movable contact-arms of switches 4I and 42 return to the fie-energized positions, i. e., to the lower contacts. By reason of the opening of switch 42, magnetic clutch 44 disengages, motor 33 stops running, relay 36 is de-energized, and the contact arms of relay 36 return to the lower-contact positions. The receiver is now tuned, well within the range of conventional automatic-frequency-control (AFC) to the frequency of the station associated with station-selector pushbutton 2; and the receiver is also in condition to respond to the succeeding action of the operator, whatever that might be.

Although the use of automatic-frequency-control (AFC) is not essential to the improved system, the illustrated embodiment does employ AFC and is so arranged that when motor 33 is running, the AFC voltage developed, in customary manner, in block I6 is shorted to ground through the upper contact of switch 4I of control relay 35. When thefrequency of local oscillator I4 reaches substantially the resonant frequency of the selected series-tuned circuit and tube 34 stops conducting and control relay 35 is cie-energized and motor 33 stops running, the automatic-fre- `vquency-controli. (AEC)A system ofthe receiver: 'is

restored to operativeA condition by the removal ofthe ground connectionr at switch 4I.

Assume that the operatornext presses stationselector pushbutton 5, thus releasing pushbutton 2. The frequency of the station of pushbutton 5 iis, say 1500 kc., which is higher than that of the station of' pushbutton 2. When pushbutton 5 is pressed, the frequency of local oscillator I4 no longer coincides with the resonant frequency of the selected series-tuned circuit and the peak amplitude of the R..-F. Voltage appearing on the grid oftube I2 is below cut-off; tube I2 therefore ceases to conduct. The bias on control tube 34 thereupon returns to zero, and control tube 34 conducts. Control relay 35 is then energized, andi the closingof switch 42 completes the circuit through armature 4S, the upper portion of field winding 41', the upper-contact of switch 49 and the left-hand contact of switch 31. Motor 33 therefore turns in a direction to increase the frequency ofV local oscillator I4. Motor 33 continuesY to turn in a frequency-increasing direction until the frequency of oscillator I4 is substantially the resonant frequency of the seriestuned circuit 65, 'i3 associated with station-selector pushbutton 5;

Assume that the operator next presses stationselector pushbutton 4'. It is being assumed throughout this descriptionA that the station-selector pushbuttons are in conventional sequential Vorder, i. e., that the frequency of tne station associated with pushbutton I is lowest and that the frequency of theY stations associated with pushbuttons` 3, t and 5 are higher in sequential order. The'frequency ofthe station of pushbutton 4 is say 1400 lic. lnthepresent example, at the time pushbutton Tis pressed, the contact-arm of switch Si" is in the left-hand position, i. e. the position assumedin the preceding examples. As indicated previously; the directionof rotation of motor 33, during station-selector pushbutton operation, is determined by the position of the contact-arm of switch 3l. With the contact-arm in the left-hand position, current flows through the upper portion ot'ield winding 41 and motor 33 rotates in a direction to increase the frequency of local oscillator I4 in the example now being described, the frequency of oscillator I4, at the time pushbutton 4 waspressed, was, however, higher than the resonant frequencyA of the tuned circuit associated with pushbutton'li, anda lower, not higher, oscillator frequency is wanted. Motor 33 continues to rotate in the frequency-increasing direction until the cores, of the multi-unit tur-ner reach the upper-frequency limit of the core stroke, corresponding to astation frequency of say 1700 kc. As the tuner cores reach the upper-frequency limit, actuating-arms 52 and 54 engage switches 3l and 38, respectively, and the contact-arms are moved to the right-hand contact positions, as viewed in the drawing. Switch 38 has no function in the operation now being described, but the movement of the contact-arm of over-center switch 3l from the left-hand to the right-hand position, opens the circuit through the upper portion of held winding il and closes the circuit through the lower'portion of the field winding. This. reverses the direction of rotation of motor and the tuner cores arenow moved in a direction' to: decrease` the frequency of the tuned circuitsofzthe'RfF. amplifier', mixer'and local oscillator stages of the receiver. Motor 33 continues to rotate in the frequency-decreasing direction untilthe frequency delivered by the local oscillator Id' is substantiallyV the resonant frequency'v of the series-tuned circuit, comprising inductance and capacitor i3, associatedwith Vstation-selector pushbutton 4. At that time, tube 72 conducts, and control tube 34 ceases to conduct, thereby stop ing the tuner at the desired point, inthe mi hier previously described.

Assume that the operator now desires to manually tune in a stationnot appearing on the stationselector pushbuttons. Assume that the frequency of the station desired` is 900 kc. and that the indi- 'cater hand of dial 38, associated` with manualtuningpushbutton e', points to 550 kc., showing that the frequency of the station last manually selected was 55) kc. It will be understood that, inthe illustrated receiver now being described, the operation of the station-selector pushbuttons does not alter theposition of the manual-tuning dial indicator. 1n, the present example, the dial 08 reads 550 but the receiveris actually tuned to 1400 kc., the frequency of the station associated with station-selector pushbutton 4.

When the operator presses manual-tuning pushbutton the connection to ground of coil i8 `f selector relay 3S is broken at the lower-contacts of pushbutton f5, and selector relay 'becomes inoperative until tuner-actuated switch 38 is operated. at either the high-frequency or lowfrequency limit ofV the tuner-core stroke, as will be described later. After depressing manualtuning pushbutton 5, the operator turns-the manual-tuning control knob in a clockwise direction to change the dial reading from 550 kc. to 900'kc., the frequency of the station he wants. In so doing, the operator increases theresonant frequency of the series-tuned circuit, comprising'variable inductance i and capacitor to the oscillator frequency corresponding to a station frequency of 900 kc; When the manual-tuning control knob is turned clockwise, the manually-operated reversing switch e9 associated therewith is moved to the right-hand position, unless already occupying that position. When selector relay 3e became inoperative, by reason of the connection to ground having been opened at the lower contacts of manual-tuning pushbutton 0, as previously described, the direction of rotation of motor 33 became governed by the position of manually-operated reversing switch e9, and not by the position of tuner-actuated reversing switch 37. When reversing switch 69 is in the right-hand position, the circuit is completed through the upper portion of eld winding 4l, and the-motor turns in a direction to increase the frequency of oscillator I4. Observe then that in the present example, the frequency of the local oscillator is increased from that corresponding to a station frequency of i400 kc., the station frequency of pushbutton fi, although-the operator desires to select a station whose frequency is only 900 lrc. The motor 33 continues to turn in the frequency-increasing direction until the cores of the tunerreach the upper-frequency limit of the core stroke atrwhich time actuating-arms 52 and 54 engage switches 3l and 3S. Switch 38 is momentarily grounded, thereby completing the circuit through coil t3 of selector relay 3%, and the selector relay is energized by current from' source le through the closed contacts of pushbutton l and switch i2 of con'- trol relay 35 which is in energized position since control tube 34 is conducting. When the movable contact-arms of selector relay 35 move to the energized or upper-contact' position, a circuit to ground through the selector-relay coil 4S is cornpleted by way` of the selector relays own switchcontacts, i. e., switch and relay 36 is held in energized condition. Switch 56, in energized position, connects the lower portion of field windthe resonant frequency of the manually variablel series-tuned circuit 56, 73. rTube 'i2 thereupon conducts and control tube 3d ceases to conduct, thus stopping the tuner motordrive and returning relays :i5-and 35 to de-energized condition.

Assume that the operator now desires to manually tune in a station whose frequency is '15G kc., which is lower than the 900 kc. to which the receiver has just been tuned. To manually tune in a lower frequency station, the manual-tuning control knob is turned in a counter-clockwise direction. When this sdone, reversing switch 69 is moved to the left-hand position, thus completing the circuit through the lower portion of field winding i? by way of the lower contact of switch relay i5 being in de-energized condition by reason of the depressed position of the Manual pushbutton t which opens the relay ground connection. Current through the lower portion of held winding 4'! causes motor s3 to rotate in a frequency-decreasing direction.

Thus far, the operation of the improved tuning system has been described by a series of examples illustrating various operating conditions. As a result, generalstaternents concerning the operation f the tuning system may now be made and clearly understood. Itiwill be seen that the improved tuning system of the present invention utilizes a portion of the output of the local oscillator to control the motorized tuning of the receiver to a station selected at a remote point by either pusnbutton or manual tuning means. Thel system is so constructed and arranged that the direction of rotation of the tuner motor is fadequately controlled. When station-selector pushbutton tuning is being used, the direction of rotation of the tuner motor 33 is controlled by the position of the tuner-actuated reversing switch 3l. When the receiver is manually tuned, as by means of a manual-tuning control knob (not shown), the direction of rotation of the tuner l motor is controlled by the position of the manually-operated reversing switch 69 associated with the manual-tuning control knob. A reversingswitch selecto-r relay 35 selects the reversing switch which is to have control. During stationseiector pushbutton operation, selector relay 3S is in energized condition; the manually-operated reversing switch '69 is then inoperative, and tuneractu-ated reversing switch 31 is operative. During manual tuning, selector relay 38 is ordinarily in die-energized condition; manually-operated reversing switch da is then operative, and tuneractuated reversing switch 3'! is inoperative. When changing from station-selector pushbutton operation to rfi-anual tuning, the manually-operated reversing switch 5S controls the direction of rotation of the tuner motor except in the case where the operator rotates the manual-tuning control knob in. one direction to move the dial toward a given frequency and the receiver is already, as a result of pushbutton operation, tuned to a frequeney which is in the opposite direction from that ofthestation desired.v In that case, the manually-operated'reversing switch Ganas initial control only, and, when the tuner cores reach:

the limit ofthe core stroke, the control of the direction of rotation of the tuner motor is taken away from manually-operatedswitch-i3d and given-to tuner-actuatedswitch Slby the action of switc-hLS'S land relay 3l in thetuning systemillustrated in the drawing, the receiver is muted whenever selector relayA isI energized condition, asis the case diuing station-selector pushbutton operation.

The muting is-accomplished by opening the speakf er circuit' at the lower contact of switch 5I of relay 35. When the selected station is tuned in,

relfay'sb` is de-energized, as has been previously described, and the speaker circuit is reestablished.

An'automoble broadcast receiver having a tuning-'system similar, except for the omission of au` tornatic-frequency-control (AFC), to that illus-- trated'invthe drawing-g and described above, has

been built, installed and tested. The results obtherein. For example; while Iliave described an inductance-tuned receiver, the tuningsystern' of the invention may be employed to equal advantage insa-1capacitance-tuned receiver.

Andwhile I` have? described motor- 33 as being a reversible center-tapped shunt-wound D. C. motor, it will' be understood that any suitable motor maybe used. If thefimproved tuning system-is-employedin an A. C. receiver, the tuner motor will ordinarily-be areversible A. C. motor.

And yWhile I lprefer touselanevacuated tube for controlftub'e 34', aegridf-controlled'gas tube may be employed, if desired, together with appropriate circuit modifications.

I have shown the biasing voltage for control tube 34 -to be obtained-from the -biasing network of the receivers push-pull amplifier. Any other suitable biasing circuit may, however, be used.`

And while other biasing means may be used for detector triode 12, a particular advantage is obtained by using the biasing method shown in the illustration and described above. It will be understood that if the biasing voltage for detector tube 12 is too large, the tube will not conduct when local oscillator I4 reaches the resonant frequency of the selected tuned circuit, and motor 33 would, in that case, continue to run. On the other -f hand, if the biasing voltage is too small, the detector tube 'I2 Will conduct over too wide a tuning range, and motor 33 may stop at a frequency not sufficiently close to the resonant frequency of the selected tuned circuit. When the biasing voltage is obtained in the manner illustrated and described, neither of the above unsatisfactory conditions will occur for the reason that the negative D. C. bias Voltage and the R. F. oscillator voltage applied to the grid of tube l2 are maintained in substantially constant relationship. Consequently, if the frequency response of local oscillator I4 is not absolutely at throughout the frequency band, the negative D. C. biasing voltage will vary in the same direction and in substantially the same proportion as the R. F. oscillator voltage picked up by coil 28, thus insuring that current passes through the detector triode l2 only at substantially the resonant frequency of the selected tuned circuit and only at the positive peaks of the R, F. voltage of said resonant frequency.

Having described my invention, I claim:

1. In the tuning system of a superheterodyne radio receiver having a tunable local oscillator; a plurality of tuned circuits at least one of which is variable; means, including station-selector push- '.f

bottons and a manually operable tuning control, for selecting one of said tuned circuits; means for comparing the frequency of said local oscillator with the resonant frequency of said selected tuned circuit; means for deriving a voltage indicative of the relationship between said compared frequencies; and means for utilizing said derived voltage to change the frequency of said local oscillator in such direction and to such an extent that said local-oscillator frequency coincides substantially with the resonant frequency of said selected tuned circuit, said voltage-utilization means comprising a reversible motor mechanically coupled to said local oscillator and means for controlling the direction of rotation of said motor, said directioncontrolling means including a tuner-actuated reversing switch to control the direction of rotation of said motor during station-selector pushbutton operation, a manually-operated reversing switch mechanically coupled with said manually-operable tuning control effective during manual tuning to effect rotation of said motor in the same sense as that in which said manually-operable tuning control is rotated, and a reversing-switch selector relay for selecting the reversing switch which is to have control of the direction of rotation of said motor, said selector relay being operative to take control away from the manuallyoperated reversing switch and to give control to the tuner-actuated reversing switch when, following station-selector pushbutton tuning, the

manually-operable tuning control is turned in a sense opposite to that in which the motor should rotate to effect said coincidence between said local-oscilator frequency and said resonant frequency of said selected tuned circuit.

2. In the tuning system of a superheterodyne radio receiver having a permeability tuned local oscillator; a plurality of adjustable tuned circuits at least one of which is variable; means, including station selector pushbuttons and a manually operable tuning control, for selecting one of said tuned circuits; means for comparing the frequency of said local oscillator with the resonant frequency of said selected tuned circuit; means for deriving a voltage indicative of the relationship between said compared frequencies; and means for utilizing said derived voltage to change the frequency of said local oscillator in such direction and to such an extent that said local-oscillator frequency coincides substantially with the resonant frequency of said selected tuned circuit, said voltageutilization means comprising a vacuum-tube-controlled motordrive including a reversible motor mechanically coupled to said local oscillator and means for controlling the direction of rotation of said motor, said direction-controlling means including a tuner-actuated reversing switch to control the direction of rotation of said motor during station-selector pushbutton operation, a manually operated reversing switch mechanically coupled with said manually-operable tuning control effective during manual tuning to effect rotation of said motor in the same sense as that in which said manually-operable tuning control is rotated,

and a reversing-switch selector relay for selecting the reversing switch which is to have control of the direction of rotation of said motor, said selector relay being operative to take control away from the manually-operated reversing switch and to give control to the tuner-actuated reversing switch when, following station-selector pushbutton tuning, the manually-operable tuning control is turned in a sense opposite to that in which the motor should rotate to effect said coincidence between said local-oscillator frequency and said resonant frequency of said selected tuned circuit.

FRANK HIMMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,182,352 Prochmow Dec. 5, 1939 2,304,871 Andrews Dec. 15, 1942 2,382,203 Chandler Aug. 14, 1945 

